Reinforced pouch type secondary battery

ABSTRACT

A pouch type secondary battery having enhanced reliability by protecting the battery from external impacts is described. A reinforcement structure may be installed on a pouch casing and an electrode assembly housed in the pouch casing. Short-circuits inside the pouch casing may be minimized. The pouch type secondary battery has an electrode assembly with positive and negative electrode plates with a separator interposed therebetween, and positive and negative terminal portions extending from the positive and negative electrode plates. A first reinforcement member is closely adhered to one or more planes of the electrode assembly. A second reinforcement member may be adhered to the pouch casing and used with or without the first reinforcement member.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/761,983 filed Apr. 16, 2010, which is a continuation of U.S. patentapplication Ser. No. 10/462,729 filed Jun. 17, 2003, now issued as U.S.Pat. No. 7,722,984, and claims the priority of Korean Patent ApplicationNo. 10-2002-0033721, filed on Jun. 17, 2002, which are all herebyincorporated by reference for all purposes as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a secondary battery, and moreparticularly, a secondary battery in a pouch casing with a reinforcementstructure.

2. Description of the Related Art

Secondary batteries are rechargeable and can be made in small sizes withhigh capacities. Typical examples of secondary batteries includenickel-metal hydride (Ni—MH) batteries and lithium (Li) secondarybatteries.

Secondary batteries are classified into cylindrical batteries using acylindrical aluminum can, rectangular batteries using a rectangularaluminum can, and pouch type batteries where the battery is accommodatedin a thin-film pouch type casing.

A pouch type secondary battery, as shown in FIG. 1, includes anelectrode assembly 10 which generates a predetermined current, and apouch casing 20 which encloses and hermetically seals the electrodeassembly 10. The electrode assembly 10 has an electrode tab 14 drawnfrom one side which is connected with a lead 15 that serves as anelectrical path leading outside. The lead 15 has a protective tape 16adhered to its surface so that it extends outside the pouch casing 20.

The pouch casing 20 includes a case body 22 having an internal space inwhich the electrode assembly 10 is retained, and a cover 24 integrallyextending from one end of the case body 22. A flange 23 is formed at theperiphery of the case body 22 and is configured to be welded with thecover 24 to hermetically seal the case body 22.

The pouch casing 20 of the pouch type secondary battery having theabove-described configuration is typically made of a metal foil andresin materials. FIG. 2 is a cross-sectional view taken along the lineI-I shown in FIG. 1. As shown in FIG. 2, the pouch casing 20 is formedof composite materials compressed such that a thermal adhesion layer 22b is formed on the inner face of a foil 22 a. The thermal adhesion layer22 b may be formed from denatured polypropylene, e.g., castpolypropylene (CPP). The foil 22 a may be made of a metal, e.g., Al. Asheathing 22 c made of a polymer resin, e.g., nylon orpolyethyleneterephthalate (PET), is formed on the outer face of the foil22 a. The thermal adhesion layer interposed between the foil 22 a andthe sheathing 22 c. Thus, the pouch casing 20 can be sealed by heatcompression in a state in which thermal adhesion layers of the case body22 and the pouch cover 24 are joined to each other.

However, since the pouch casing having the above-described configurationis very thin, there is a limitation in protecting the electrode assemblyhoused in the pouch casing.

In particular, in such a pouch casing, the thickness of a metal foilprovided for the purpose of maintaining the strength of the casing isonly several tens of micrometers. Accordingly, the metal foil is veryweak against external impacts.

When a battery using the conventional pouch casing is cut or shocked bya sharp tool, the safety of the battery may be impaired, resulting inpoor reliability.

In such a pouch casing, the melting point of the thermal adhesion layermade of, for example, CPP, is about 130° C. to 140° C., and the meltingpoint of a separator of the electrode assembly housed in the pouchcasing is also about 130° C. to 140° C. The temperature of thermallywelding a case body and a pouch cover of the pouch casing is about 180°C. to 210° C. Thus, during thermal welding of the pouch, the thermaladhesion layer and the separator may melt, or the separator may befusibly fixed with the thermal adhesion layer. Also, the thermaladhesion layer melts exposing the Al metal film inside, so that the Almetal film may be short-circuited from the electrode assembly.

In a lithium polymer secondary battery, a stacked electrode assembly ishoused in the pouch casing and has a bi-cell structure, as shown in FIG.3. The bi-cell structure is a unit of an electrode assembly, and isgenerally constructed such that a positive electrode sheet 11 is stackedon both faces of a negative electrode sheet 12 with a separator 13interposed between each of the positive and negative electrode sheets 11and 12. As shown in FIG. 3, the area of each separator 13 defining thepositive and negative electrode sheets 11 and 12 is greatest and thearea of the positive electrode sheet 11 is smallest. A plurality ofbi-cell laminates is stacked to form an electrode assembly 10.

As described above, when the electrode assembly 10 having a plurality ofbi-cell laminates stacked is housed in a pouch casing, the batteryswells due to gas generated inside the battery as the battery isrepeatedly charged and discharged. When gas is generated insideelectrode sheets of the electrode assembly, the electrode sheets mayswell in a direction indicated by an arrow shown in FIG. 3, while theseparator 13 shrinks somewhat. Accordingly, the positive electrode sheet11 and the negative electrode sheet 12 may be short-circuited from eachother at their edges.

Therefore, it is necessary to protect the battery from short-circuit dueto swelling of the electrode assembly.

U.S. Pat. No. 6,042,966 discloses a battery structure for preventingelectrical short between an electrode tab exposed outward and a cut edgeof a pouch, wherein the pouch comprises an outer lamination layer madeof a packaging insulator film on the outer face of a metal foil, and aninner lamination layer having a polyamide layer made of, for example,nylon, and a thermal adhesion layer sequentially formed on the innerface of the metal foil.

U.S. Pat. No. 6,106,973 discloses a pouch formed by folding a laminatedfilm having an Al film at the inner side and a polypropylene film at theouter side on both sides of an electrode assembly.

The above-described pouches having thin films still have severaldrawbacks including poor structural stability. Also, in the case ofusing a stacked electrode assembly, short-circuit between electrodes mayoccur due to swelling of the electrode assembly.

SUMMARY OF THE INVENTION

Accordingly, the invention provides a pouch type secondary batteryhaving enhanced reliability by protecting the battery from externalimpacts by separately installing a reinforcement structure on a pouchcasing and on an electrode assembly housed in the pouch casing.

Also, the present invention provides a pouch type secondary batteryhaving enhanced reliability by minimizing a short-circuit inside a pouchcasing.

In accordance with an aspect of the present invention, there is provideda pouch type secondary battery comprising an electrode assembly havingpositive and negative electrode plates with a separator interposedtherebetween. Positive and negative terminal portions extend from thepositive and negative electrode plates. A first reinforcement member isadhered to at least one plane of the electrode assembly. A pouch casinghouses the electrode assembly and the first reinforcement member andexposes the positive and negative terminal portions to the outside. Thepositive and negative terminal portions are insulated from each other atsealed portions of the pouch casing.

The first reinforcement member may be a metal foil. Also, the firstreinforcement member may have a first layer made of a metal foil and asecond layer made of an adhesive resin material. The first reinforcementmember may have a fiber reinforced resin material. Further, the firstreinforcement member may have an insulating tape. The firstreinforcement member may have a thermal adhesion layer adhered to aplane facing the electrode assembly by heat. Also, the firstreinforcement member may be fixed to the electrode assembly by aninsulating tape.

Further, an insulating terminal cover having insertion holes into whichthe positive and negative terminal portions may be inserted to beexposed outside may be installed at lateral planes of the electrodeassembly from which the positive and negative terminal portions extend.

In accordance with another aspect of the present invention, there isprovided a pouch type secondary battery including an electrode assemblyhaving positive and negative electrode plates with a separatorinterposed. Positive and negative terminal portions extend from thepositive and negative electrode plates. An insulating tape is adhered toat least one plane of the electrode assembly. A pouch casing houses theelectrode assembly adhered to the insulating tape and exposes thepositive and negative terminal portions to the exposed outside. Thepositive and negative terminal portions are insulated from each other atsealed portions of the pouch casing.

An insulating terminal cover having insertion holes into which thepositive and negative terminal portions may be inserted to be exposedoutside may be installed at lateral planes of the electrode assemblyfrom which the positive and negative terminal portions extend.

In accordance with still another aspect of the present invention, thereis provided a pouch type secondary battery including an electrodeassembly having positive and negative electrode plates with a separatorinterposed therebetween. Positive and negative terminal portions extendfrom the positive and negative electrode plates. A pouch casing housesthe electrode assembly and exposes the positive and negative terminalportions to the outside. The positive and negative terminal portions areinsulated from each other at a sealed portion of the pouch casing. Asecond reinforcement member is adhered to at least one plane of theinternal surfaces of the pouch casing.

The second reinforcement member may be a metal foil. Also, the secondreinforcement member may have a third layer made of a metal foil and afourth layer made of an adhesive resin material. The secondreinforcement member may have a fiber reinforced resin material.Further, the second reinforcement member may have an insulating tape.The second reinforcement member may have a thermal adhesion layeradhered to a plane facing the electrode assembly by heat. Also, thesecond reinforcement member may be fixed to the electrode assembly by aninsulating tape.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings.

FIG. 1 is an extracted perspective view of a conventional pouch typesecondary battery.

FIG. 2 is a cross-sectional view illustrating various materials of ageneral pouch.

FIG. 3 is a cross-sectional view illustrating a bi-cell stackedstructure of a general stacked electrode assembly.

FIG. 4 is an exploded perspective view of a pouch type secondary batteryhaving a stacked electrode assembly according to an embodiment of thepresent invention.

FIG. 5 is an exploded perspective view of a pouch type secondary batteryhaving a wound electrode assembly according to another embodiment of thepresent invention.

FIGS. 6, 7, 8, and 9 are perspective views illustrating electrodeassemblies to which first reinforcement members according to variousexamples of the present invention are closely adhered.

FIGS. 10A, 10B, 10C, and 10D illustrate the state in which an insulatingtape and a terminal cover are coupled to an electrode assembly accordingto another embodiment of the present invention.

FIGS. 11, 12, and 13 illustrate the state in which a secondreinforcement member is closely adhered to an electrode assemblyaccording to other embodiments of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will be described withreference to the appended drawings.

FIG. 4 is an exploded perspective view of a pouch type secondary batteryaccording to an embodiment of the present invention. As shown in FIG. 4,an electrode assembly 40 is of a stacked type in which a plurality ofbi-cell stacked structures each having positive and negative electrodeplates 41 and 42 with a separator 43 interposed therebetween, arestacked. The stacked electrode assembly 40 shown in FIG. 4 is typicallyused in polymer lithium secondary batteries. The positive electrodeplate 41 is formed by thermally compressing a positive electrode sheetcontaining a positive electrode active material comprising lithium oxideon at least one plane of a positive electrode current collector made ofa metal foil, e.g., an aluminum foil. The negative electrode plate 42 isformed by thermally compressing a negative electrode sheet containing anegative electrode active material comprising a carbon material on atleast one plane of a negative electrode current collector made of ametal foil, e.g., a copper foil. The electrode assembly 40 is housed ina pouch casing 30, and an electrolytic solution is impregnated into theelectrode assembly 40, followed by sealing the pouch casing 30, therebyforming a secondary battery.

Electrode tabs 44 drawn from each of the electrode plates 41 and 42 areprovided at one side of the stacked electrode assembly 40, and electrodelead portions 45 are welded to the electrode tabs 44. The positiveelectrode tabs 44 a are drawn from the positive electrode plate 41 and apositive electrode lead 45 a is welded to the positive electrode tabs 44a. Negative electrode tabs 44 b are drawn from the negative electrodeplate 42 and a negative electrode lead 45 b is welded to the negativeelectrode tabs 44 b. The positive and negative electrode leads 45 a and45 b are exposed outside the pouch casing 30 even after being sealed,forming electrode terminals in cooperation with the electrode tabs 44and the electrode lead portions 45. A polymeric protective tape 46 forprotecting the electrode terminals is adhered to the electrode leadportion 45 so that the electrode terminals are insulated from each otherwhen the case body 32 and a pouch cover 34 are sealed.

The electrode assembly may be a wound electrode assembly 50 where apositive electrode plate 51 and a negative electrode plate 52 are woundwith a separator 53 interposed therebetween, as shown in FIG. 5. Thewound electrode assembly 50 shown in FIG. 5 is typically used in lithiumion batteries and is configured such that the separator 53 is interposedbetween the positive and negative electrode plates 51 and 52 and theresultant product is wound.

The positive electrode plate 51 is formed by coating a positiveelectrode composite slurry containing a positive electrode activematerial, e.g., lithium oxide, on a positive electrode current collectormade of a metal foil, e.g., an aluminum foil. The negative electrodeplate 52 is formed by coating a negative electrode composite slurrycontaining a negative electrode active material, e.g., a carbonmaterial, on a negative electrode current collector made of a metalfoil, e.g., a copper foil. The wound electrode assembly 50 is housed inthe pouch casing 30 and sealed except for an electrolytic solutioninjection hole. An electrolytic solution is injected through theelectrolytic solution injection hole into the pouch casing and theelectrolytic solution injection hole is sealed, thereby forming asecondary battery.

Electrode tabs 54 are drawn from each of the electrode plates 51 and 52of the wound electrode assembly 50. Positive electrode tabs 54 a aredrawn from the positive electrode plate 51 and negative electrode tabs54 b are drawn from the negative electrode plate 52. Likewise in thestacked electrode assembly 40, a polymeric protective tape 56 forprotecting each of the electrode terminals is adhered to each of thepositive and negative electrode tabs 54 a and 54 b, thereby formingpositive and negative electrode terminals, respectively.

In the stacked electrode assembly 40 and the wound electrode assembly50, as shown in FIGS. 4 and 5, a first reinforcement member 60 isclosely adhered to at least one plane thereof and accommodated in apouch casing 30. The pouch casing 30 includes a case body 32, recessedto accommodate the electrode assembly 40 or 50, and a pouch cover 34covering the case body 32 to be sealed. The shape of the pouch casing 30is not particularly limited. Although not shown, a pouch casing havingan opening in its one plane to be sealed, may be used to accommodate anelectrode assembly. In this case, a seal portion is provided. Forconvenience, the invention will now be described with regard to theabove-described pouch casing having a case body and a pouch cover. Oneskilled in the art will recognize that the invention has broadapplication to a variety configurations and is not limited to theembodiments described herein.

In the above-described pouch type secondary battery, the pouch casing 30is preferably formed of a composite foil of a metallic material and aresin material. That is, the pouch casing 30 may be formed of acompressed composite material consisting of denatured polypropylene,e.g., cast polyproplylene (CPP), which is a thermally fusible polymerresin, inward with respect to a metal foil, e.g., an aluminum foil, andanother CPP layer interposed between the metal foil and a resin materiallayer formed of nylon or polyethyleneterephthalate (PET). Thus, thepouch casing 30 can be sealed by thermal compression in a state in whichthe CPP layers are contacted with each other.

Next, a first reinforcement member closely adhered to the electrodeassembly will be described. In the present invention, the firstreinforcement member may be applied to both a stacked electrode assemblyand a wound electrode assembly. The invention will be, for convenience,described with regard to the stacked electrode assembly. The features ofthe present invention are also applicable to the wound electrodeassembly.

As shown in FIG. 4, a first reinforcement member 60 is closely adheredto at least one plane of the electrode assembly 40. In a preferredembodiment shown in FIG. 4, the first reinforcement member 60 is shapedof a panel so as to contact the upper face or bottom face of theelectrode assembly 40. The first reinforcement member may have a firstlayer 60 a made of a metal foil, e.g., aluminum, iron or stainlesssteel, and a second layer 60 b made of an adhesive resin material, e.g.,CPP, on a plane of the first layer 60 a facing the electrode assembly40. The second layer 60 b may be formed by laminating an adhesive resinfilm on the first layer 60 a made of a metal foil, or coating anadhesive resin material thereon. Also, the second layer 60 b can beformed on the other plane of the first layer 60 a opposite to the planefacing the electrode assembly 40.

The above-described first reinforcement member 60 is tightly fixed tothe electrode assembly 40 such that the second layer 60 b is adhered tothe electrode assembly 40. If the second layer 60 b is formed of athermally adhesive material as described above, thermal compression canbe employed. However, the second layer 60 b made of a general adhesiveresin can be adhered to the electrode assembly 40 simply by pressing thesame onto the electrode assembly. Also, in the first reinforcementmember 60, the first layer 60 a may be formed of a fiber reinforcedresin material rather than the metal foil.

The first reinforcement member may be formed of a single material ofeither a metal foil or a fiber reinforced resin material.

As shown in FIG. 6, a first reinforcement member 61 may be fixed to theelectrode assembly 40 using an insulating tape 62. Although not shown,the first reinforcement member can be accommodated in a pouch case in astate in which it is in close proximity to the electrode assembly butdoes not contact the electrode assembly.

Also, a first reinforcement member 63, as shown in FIG. 7, may be formedof an insulating tape to be adhered to at least one plane of theelectrode assembly 40. Such a first reinforcement member may havevarious shapes. As shown in FIGS. 8 and 9, the first reinforcementmember may be formed on lateral surfaces of the electrode assembly 40.As shown in FIG. 8, the first reinforcement member is adhered to theelectrode assembly 40 such that a lower reinforcement element 65 closelycontacts the bottom surface, lateral surfaces and rear surface of theelectrode assembly 40, and an upper reinforcement element 64 closelycontacts the upper surface of the electrode assembly 40. Although notshown in the drawing, an insulating tape may be wrapped around the firstreinforcement member for fixedly adhering the reinforcement member tothe electrode assembly 40. Referring to FIG. 9, the first reinforcementmember may be thermally compressed to the electrode assembly 40 suchthat an upper reinforcement element 64′ closely contacts the uppersurface and lateral surfaces of the electrode assembly 40, and a lowerreinforcement element 65′ closely contacts the bottom surface, lateralsurfaces and rear surface of the electrode assembly 40. Also, the firstreinforcement member may be fixed with the electrode assembly 40 usingan insulating tape to then be closely adhered thereto. The upper andlower reinforcement members of the first reinforcement member may beformed of insulating tapes only.

The first reinforcement member is closely adhered to planes of anelectrode assembly, thereby more effectively protecting the electrodeassembly against external impacts when the electrode assembly isaccommodated in a pouch casing. The electrode assembly may becomeswollen due to swelling occurring during an initial charging anddischarging period of a battery. A short-circuit may occur at the edgesof an electrode assembly due to swelling of the electrode assembly.Swelling of the electrode assembly can be prevented by closely adheringthe reinforcement member to the outer surfaces of the electrodeassembly, thereby reducing a change in external dimensions due toswelling.

FIGS. 10A, 10B, 10C, and 10D illustrate a reinforcement member with aninsulating tape adhered to the lateral planes of the electrode assembly40. As shown in FIG. 10A, a side insulating tape 66 is adhered to bothlateral planes of the electrode assembly 40. As shown in FIG. 10B, arear insulating tape 67 is adhered to the rear plane of the electrodeassembly 40. Although FIG. 10B shows lateral insulating tape 66, theinvention is not limited thereto and may use only the rear insulatingtape 67.

As shown in FIGS. 10A and 10B, adhering insulating tape to the lateralplanes of the electrode assembly 40 is particularly advantageous for astacked electrode assembly. A stacked electrode assembly is prone toshort-circuit between positive and negative electrodes due to swelling.Short-circuit at edges of the electrode assembly can be prevented bysimply adhering an insulating tape to the lateral planes of theelectrode assembly.

As shown in FIGS. 10C and 10D, the reinforcement member may have aninsulating terminal cover 68 at the side where an electrode lead 45 isformed. The insulating terminal cover 68 may have insertion holes 68 ainto which the electrode leads 45 are inserted. The insulating terminalcover 68 can be coupled to the front face of the electrode assembly 40using a separate insulating tape 69. As shown in FIG. 10D, theinsulating terminal cover 68 allows the electrode lead 45 to be drawnout and protects the electrode tab 44 bent inside. Thus, the terminalcover 68 serves as both an insulator and a reinforcement member. Theterminal cover 68 can be applied to the above-described previousembodiments of the present invention.

A reinforcement member may be formed directly in a pouch case as well asat the electrode assembly.

As shown in FIGS. 11 and 12, a pouch type secondary battery can befurther reinforced by providing a second reinforcement member 70 closelyadhered to at least one plane of internal faces of a pouch casing 30where an electrode assembly is accommodated and sealed.

The second reinforcement member 70, as shown in FIG. 11, may have abottom reinforcement element 72 adhered to the bottom of a case body 32of the pouch casing 30, and a top reinforcement element 71 adhered tothe internal ceiling of the pouch casing 30. The case body 32 and apouch cover 34 of the pouch casing 30 are coupled to each other at aflange 33 of the case body 32. Thus, the top reinforcement element 71 isnot preferably adhered to a periphery 35 of the pouch cover 34,corresponding to the flange 33 of the case body 33.

Unlike the plane-shaped bottom reinforcement element 72 shown in FIG.11, a bottom reinforcement element 73 may be formed such that it isclosely adhered to the internal faces of the case body 32, as shown inFIG. 12. In this case, the height of a lateral plane 73 a at whichelectrode terminals are sealed is preferably smaller than that of theother plane 73 b.

Referring to FIG. 13, the second reinforcement member 70 can also beapplied to a pouch casing 80 having a round bottom 82 a. As shown inFIG. 13, a bottom reinforcement element 75 having the same shape as theround bottom 82 a is closely adhered to the bottom 82 a of the case body82. Also, although not shown, a reinforcement member can be provided atthe front and/or rear planes of the pouch casing 80.

The second reinforcement member can be applied to any type of a pouchcasing. For example, the second reinforcement member may be formed of ashape corresponding to that of the internal face of the pouch casing andclosely contacted thereto.

Like the first reinforcement member, the second reinforcement member canbe formed of a metal foil, a fiber reinforced resin material or aninsulating tape, and can be closely adhered to the internal face of thepouch casing by thermal compression using an adhesive resin, except forthe insulating tape which has intrinsic adhesiveness.

As described above, the present invention has the following advantages.

First, the safety of a pouch type secondary battery against externalimpacts can be enhanced, thereby increasing the reliability of thebattery.

Second, internal short-circuit of a pouch casing, can be prevented.

Third, an reinforcing effect of a battery can be effectuated by a simplestructure, thereby improving manufacturability.

While this invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A pouch type secondary battery comprising: an electrode assemblyhaving positive and negative electrodes plates with a separatorinterposed therebetween, and positive and negative terminal portionsextending from the positive and negative electrodes plates; a firstreinforcement member adhered to at least one plane of the electrodeassembly; and a pouch casing in which the electrode assembly is housed,wherein the positive and negative terminal portions extend outward fromthe pouch casing, the positive and negative terminal portions beinginsulated from each other at a sealed portion of the pouch casing.